1. Field of the Invention
The present invention relates to an image pickup apparatus and an image pickup method. In particular, the present invention relates to an image pickup apparatus with an automatic focusing function and an image pickup method.
2. Description of the Related Art
An image pickup apparatus with an automatic focusing (AF) function performs automatic focusing by converting the contrast of a subject image formed on a CCD into an electric signal, amplifying the electric signal using a highpass filter (HPF), analyzing the waveform of the amplified electric signal, and focusing on the subject according to the analysis result.
Specifically, in consideration of the fact that the waveform of the amplified electric signal is gentle when the image pickup apparatus is not focused on the subject, and the waveform of the magnified electric signal is steep when the image pickup apparatus is focused on the subject, the image pickup apparatus is adapted to move the lens to a position where the waveform becomes steepest is obtained among a plurality of shot subject images in driving the lens.
In the above automatic focusing, normally a central part or a plurality of areas on the CCD plane are set as a ranging area.
The conventional image pickup apparatus with the automatic focusing (AF) function detects the distance to the whole face of a person as a subject set as the ranging area and adjusts the focal position, lens focal distance, and aperture value so that the detected distance to the subject can be within the depth of field. An example of the conventional image pickup apparatus is described in Japanese Patent Publication No. 3164692.
Here, the depth of field is the range in the direction of depth over which a sharp image of the subject can be produced (focusing range). The depth of field varies according to the distance from the image pickup apparatus to the subject, lens focal distance, and aperture value. When the distance from the image pickup apparatus to the subject is long, the lens focal distance is short, and the aperture value is large, the image pickup apparatus can produce a sharp image of the subject without performing automatic focusing because the distance from the image pickup apparatus to the subject is within the depth of field.
Another conventional image pickup apparatus is provided with a distance detecting device which detects the distance from the image pickup apparatus to a subject based on the size of an area occupied by the subject on a shooting screen on which a shot subject image is formed. An example of this image pickup apparatus is described in Japanese Laid-Open Patent Publication (Kokai) No. 2003-75717.
However, the above conventional image pickup apparatuses use the same automatic focusing method irrespective of whether automatic focusing is required or not, and therefore cannot accurately perform automatic focusing and reduce the time required for automatic focus scanning in automatic focusing.